This invention pertains to the purification of aromatic hydroxy compounds obtained by the cleavage of benzylic hydroperoxides. More particularly, it pertains to a process for purifying hydroquinone made by the cleavage of p-diisopropylbenzene dihydroperoxide.
The state of the present technology is represented by U.S. Pat. Nos. 3,884,983 and 3,968,171. The basic process common to these patents is the acid-catalyzed cleavage or rearrangement of p-diisopropylbenzene dihydroperoxide in a benzene/acetone solvent to hydroquinone and acetone followed by neutralization of the acid catalyst and separation of the hydroquinone from the solvent and by-product impurities.
In U.S. Pat. No. 3,968,171, the separation is accomplished by distilling the acetone off and mixing the distillation bottoms with water; extracting impurities from the bottoms with benzene; and treating the aqueous hydroquinone-containing phase by evaporation, crystallization, centrifugation, and drying.
U.S. Pat. No. 3,884,983 adds the steps of maintaining a reducing atmosphere in the system, carbon treating the concentrated aqueous hydroquinone solution, and purifying recycled water in ion-exchange beds.
Selective hydrogenation of the neutralized rearrangement reactor effluent to prevent formation of polymeric impurities in the distillation step downstream of the reactor is added by U.S. Pat. No. 3,895,079. Hydrogenation of technical grade hydroquinone can produce photograde (high purity) hydroquinone according to German Pat. No. 2,505,271.
Extraction of the aqueous distillation bottoms with a halogenated hydrocarbon (1-3 C) instead of benzene has been proposed as a way to purify hydroquinone in U.S. Pat. No. 3,798,277.
It is thus the purification of the rearranged product which has been the subject of a long continuing effort on the part of those in the field. The reason for this is that the hydroquinone must be a white crystal or crystalline power which meets ASA specification PH 4.126-1962 in order to be photograde. A high standard for whiteness is imperative for photograde material. Hydroquinone is used widely as the main ingredient in black and white film print developing. The purification processes are directed toward improved crystallization and whiteness.
Hydroquinone is also useful as a polymerization inhibitor and as an antioxidant. Hydroquinone itself and derivatives, such as 2,5-di-tert-butylhydroquinone and butylated hydroxyanisole (BHA), are used for the prevention of oxidation in animal or plant fats and aviation fuels.
By-products of the rearrangement reaction, referred to as tars, are believed to be the major impediment to high purity. Among the components of these tars are: p-isopropylphenol, .alpha.-hydroxy-p-isopropylphenol, p-diisopropylbenzene, p-isopropenylphenol, isopropenylacetophenone, and dimers and trimers of the product and by-products.